802 THE DISTRIBUTION OF SPECIES BY OFFSHOOTS. considerable an increase and distribution as Strawberries. The accompanying table gives the length of runners and shoots of some well-known species in which the formation and rapid distribution of offshoots is particularly noticeable on suitable substrata. Saxifraga Aizoon , „ cuneifolia , „ Geum , „ fiageUaris Viola odorata Arahis proewrrens, Androsace sarmentosa Ajuga reptans , , Sieraeium flageUare . Centimetres. 4 10 12 13 16 18 20 30 Lycopodi-mn a/nnoti/n/um. Saxifraga sarmentosa Ranunculus Flammmla . Geum reptans .... Glyceria fluitans . . IMhosperrwwm pv/rpureo- cceruleum . , , , Ranunculus reptans , , Tiarella cordifolia Vmea Libanotica , . . Centimetres. 30-40 40 ^50 56 60 65 66 Centimetres Vinca herbacea. . . . , 70 Fragaria Indica , . , 85 Potentilla anserina 110 Glechoma hederacea . . 126 Potentilla reptans , . . . 130 Rubus saxatilis. . . 140 Fragaria vesca , , . . 150 Vinca major , . 200 Rubus Radula . . . , 300 „ bifrons . . . 650 In those cases in which plants change their position by the development of offshoots in any direction, whilst they die off in the opposite one, progress is always restricted. The offshoots penetrate only by slow degrees in the surrounding soU, and many years elapse before a space of 100 metres is traversed in this way. The change of position is much more rapid when the offshoots become detached from their place of origin and are carried to a new spot by special mechanisms of transit, by currents of water, the wind, or finally by the help of men or animals. In this way it may happen that single detached cells, cell-groups, buds, and shoots may be carried vastly further than 100 metres in a few minutes, through long valleys, over steep precipices, or even over high mountain ridges. This rapid distribution is not indeed so certain in its result as the slower mode of progression. It may easily happen that the wind or water current lands the detached offshoot on some spot where further development is impossible, where it must inevitably perish. Appa¬ rently, however, this disadvantage is compensated for by the immense quantity of such detached offshoots. Again, there are plants which form two kinds of offshoots, those which propagate slowly but surely, which are few in number, and others, developed in large numbers, which are distributed rapidly but less certainly. Only a very small proportion of plants develop offshoots which after they become detached reach a new locality spontaneously, by means of special organs of motility. This class of brood-body is always aquatic and of very small size, and its development can only be followed under the microscope. The best-known examples are Fungi, belonging to the Saprolegniaceae and Chytridiaceae, the dark green Vaucherias, and other species of Algae. The Saprolegnias are sapro¬ phytes growing in and on the bodies of animals which have died in the water— not only fish, crustaceans, and insect larvae, but also birds. They form delicate, thread-like, tubular hyphae, which ramify repeatedly, and part of which penetrate into the corpse like a root-plexus, while the rest rise up above the body in the form of white or grey felt, which floats in the water. Single tubular erect hyphae assume a knob or club-shaped form, and their protoplasm divides up into numerous portions. Ultimately the club-skaped tube opens at the apex, and the little proto-